Section III., 1913. 139] Trans. R S.C. 



On the Electrical Conductivity Imparted to Liquid Air by 

 Alpha Rays.'^ 



By Professor J. C. McLennan and Mr. David A. Keys. 



I. Introduction. 



In the published account of then* experiments on the measure- 

 ment of the dielectric constants of different liquefied gases, a numbei 

 of investigators including Linde,t Dewar and Fleming,^ and Hasen- 

 ohrl,* have drawn attention to the high insulating qualities possessed 

 by such liquids. In particular Fleming and Dewar have shewn that 

 a small condenser when immersed in liquid air and charged with a 

 Wimshurst electrical machine held its charge perfectly for a period 

 of some minutes. Quite recently too, Zeeman^ in studying the Kerr 

 phenomenon in liquid air found when the latter was freed from small 

 ice and carbonic dioxide crystals by filtration, and when precautions 

 were taken to prevent the generation of gas bubbles between the 

 electrodes, electric fields as high as 90,000 volts per cm., and even 

 higher ones could be maintained quite readily in the liquid. 



Fleming and Dewa^; in the course of their experiments made a 

 determination of the dielectric constant of liquefied air and also of 

 that of liquid oxygen. The latter they found to be 1-495. If we 

 assume the density of gaseous oxygen at 15° C. and 760 mm. pressure 

 to be 0-00134 (and its density at -182° C, consequently to be 0-00424) 

 and its dielectric constant at 0°C and 760 mm. pressure to be 1-00059, 

 it follows by applying the Clausius Mosotti relation, — that K — 1 is 

 proportional to the density of the gas, — that the dielectric constant 

 of gaseous oxygen at -182° C. and 760 mm. pressure should be ap- 

 proximately 1-0018. 



Moreover as the density of liquid oxygen is about 1 • 1375, it fol- 

 lows if we assume the Clausius Mosotti's Law to hold continuously 

 in passing from the gaseous to the liquid phase, that the dielectric 

 constant of liquid oxygen should be approximately 1-4824. This it 

 will be seen is very close to the value found by Dewar and Fleming 

 in their experiments. 



*Read before the Royal Society of Canada, May 2Sth, 1913. 



tLinde, Wied. Ann. 56, p. 546, 1895. 



i^Dewar and Fleming, Proc. Roy. Soc, London, p. 358, Vol. 60, 1896. 



* Ilasenohrl, Leiden. Comm. No. 52, Proc. Ams. Akad., 11, p. 211. 



• Zeeman, Proc. Amst. Akad, of Sc, Jan. 2-1, 1912, p. 650. 



